The present invention relates to portable label printing and applying machines for printing and applying labels to commodities, and more particularly to ink supply devices for such labeling machines for uniformly inking the printing surface of a printing head.
Most labeling machines have a printing head. Most such machines include a device for supplying ink to the printing surface of the printing head. In most ink supply devices, an inking roller is attached to the leading end of a spring biased pivotally mounted arm. The inking roller rolls over the printing surface under spring pressure as it supplies the ink.
An inking device that relies upon spring pressure upon the inking roller has several drawbacks. Aging of the spring lessens its biasing force and reduces the pressure of the inking roller on the printing surface. This will cause deterioration of the ink application and in the printing quality. Imprinted indicia will be dimmed and may not print in part.
The weakened spring will cause less ink to be pumped from the inking roller. Such pumping occurs when the roller is allowed to bulge as it returns to shape from being depressed by the types. Ink which might otherwise be confined at the center portion of the roller is pumped out. The biasing force of the spring is liable to vary with the strength of the actuating force of the inking device. In the worst case, the inking roller may have no contact with the printing surface during the inking operation.
Abrupt gripping of an actuating hand lever may cause irregular contact of the inking roller on the printing surface. The resultant non-uniform inking is not suitable for printing the complex, detailed indicia, such as bar codes, that are now in use.
Recently, the so-called "POS (Point of Sale) System" has been developed. Information encoded in the form of characters, such as bar codes or OCR letters, are printed on labels to be applied to commodities. This information is later automatically read out by an optical character-reading machine which is connected to a computer. The operating material such as goods in stock, amount of sales, pursuit of customers by goods or gain calculations is recorded in and processed by the computer. Highly precise imprinting of labels is required in order that the characters be accurately read by the optical character-reading machine. For this reason, the ink supply to the printing surfaces of the printing heads should be adequate in quantity and uniformly distributed.
To properly ink all types in a plurality of print heads, it has become customary to use a plurality of inking rollers. Where only one inking roller is used for inking the plurality of printing heads, it is quite difficult to supply an adequate quantity of ink uniformly to all of the printing surfaces of the respective printing heads. This results in irregularities in the print.
In accordance with the recent developments in the portable labeling machine art, the ink supply step should be accomplished before the printing of a label by the printing head. The supplying of ink should be accelerated to permit higher speed printing. For this purpose, it is found difficult to effect sufficient supply of ink with use of a single ink-impregnated roller. Thus, at least two ink-impregnated rollers are useful in certain portable labeling machines.
Use of a number of rollers increases the gripping force required for gripping the hand lever to its full stroke and increases labeler operator fatigue. This problem occurs because the plural inking rollers have to roll over the printing surfaces and be depressed to the desired extent on their outer peripheries.
The gripping force required of the operator is increased in proportion to the scale and number of the depressions in the inking rollers which must be forcibly formed by the interactions between the types being inked and the inking rollers. The required gripping force may exceed the strength of the operator of the hand labeler.
One additional way to overcome the resistance to the motion of the inking roller is to cause it to move faster or to more rapidly grip and release the hand lever. If the hand lever is gripped and released at a high speed, the imprint on the labels is thinner than when the hand lever is gripped and released at a lower speed.
If there are irregularities in the diameters or shapes of the inking roller or if the roller diameters or shapes change as a result of use and wear or they are unpredictably enlarged during ink impregnating operation, it may be difficult to properly and uniformly supply ink to the printing surfaces with inking rollers.